This invention relates to a method of forming a fluorescent screen of a color picture tube, more particularly a mosaic or stripe shaped pattern of light absorbing material,that is, a pattern of so-called black matrix surface.
As disclosed in Japanese patent publication No. 218/1971 corresponding to U.S. Pat. No. 3,558,310 of RCA, according to a prior art method of forming a black matrix surface pattern, a photosensitive film is forced on the inner surface of a faceplate of a color picture tube, the photosensitive film is exposed to light through a shadow mask, the film is developed to remove unexposed portions to thereby form a desired pattern, a suspension of such a light absorbing material as graphite is coated on the remaining exposed portions and portions of the inner surface of the faceplate corresponding to unexposed portions, the pattern is then treated with such an etchant as an aqueous solution of hydrogen peroxide or sodium hypochlorite to swell and make brittle the photosensitive material which has been hardened by light exposure, and finally the photosensitve material which became brittle is peeled off together with the light absorbing material thereon by developing, for example, washing with water, thus forming a black matrix surface having a pattern of the light absorbing material coated on the inner surface of the faceplate. There has also been available a method utilizing a positive type photosensitive material whose light-exposed portions can be removed by developing or a method wherein a number of triads of phosphors are applied to predetermined positions prior to the formation of the light absorbing pattern, and a photosensitive material which is rendered, by light exposure, insoluble to water is coated along with a light absorbing material onto portions where the triads are absent and then exposed to light from the front of the faceplate to form a pattern of light absorbing material.
These methods, however, accompany various problems when forming the black matrix surface. More particularly, the method disclosed in Japanese patent publication No. 218/1971 requires a long processing time and moreover, the size of the openings formed by removal of the exposed portions of the photosensitive film tends to become larger than the size of the exposed images of the exposed portions owing to the etching treatment. Moreover, the etchant corrodes such mechanical devices as a suspension coating machine. Positive type photosensitive material is not only expensive but also dangerous because it requires an organic solvent in use. According to the front exposure method, the configuration of the openings of the pattern where the light absorbing material is to be applied is affected by the granular contour of the phosphor layer previously formed so that the contour of the openings becomes extremely irregular, thus making it difficult to obtain clear picture images.